Porous metal articles of differential permeability



Aug, 1966 L. H. MOTT 3364 126 Filed Sept. 11, 1964 POROUS METAL ARTICLESOF DIFFERENTIAL PERMEABILITY 5 Sheets-Sheet 1 LAMERT H. MOT? azafimATTORNEY L. H. MO'TT Aug, 9, 1966 POROUS METAL ARTICLES OF DIFFERENTIALPERMEABILITY 5 Sheets-Shea: 2

FllBd Sept 11, 1964.-

INVENTORI LAMBERT H. MOT? 0% m" Mk ATTOR NEY L. H. MOTT POROUS METALARTICLES OF DIFFERENTIAL PERMEABILITY 5 Sheets-$heet 5 Filed Sept.

FEG. E4

INVENTOR.

LAMBERT H. MQTT BY @zfwv ATTGRNEY United States This is acontinuation-in-part of application Serial No. 862,522, filed December29, 1959, now abandoned.

This invention relates to porous materials in general, and, moreparticularly, to porous metal objects which can be made so that theyvary in their permeability from one area to another to control the flowof a liquid or a gas therethrough.

In recent years porous metals of many kinds have been made, such asporous stainless steel, porous nickel, porous bronze, etc. A well knownexample of the formation of a porous metal would be the following. Afine metal powder, such as 347 stainless steel, is mixed with an evenfiner stearate powder so that the grains of metal become coated with thestearate. The coated grains of the stainless steel powder may then bepressed lightly together to hold their shape and they are then sinteredin a furnace in a controlled atmosphere at a temperature of about 2200F. This bonds by solid state diffusion the individual grains together attheir points of contact. The resulting porous metal product may befurther rolled or coined to final precise dimensions, density, and poresize. It will have a tensile strength of from 7,000 to 20,000 pounds persquare inch and its porosity will vary according to the grain size ofthe metal being used, the degree to which the powder was compressed, andmany other factors.

Sheets of porous metal formed in this manner may be Welded or otherwiseconventionally fabricated into shapes. In addition, molds may be used todirectly form articles in a wide variety of shapes from metal powders.These forms may then be removed from the mold and sintered in the mannerthat has been described. Using these methods and a wide variety ofmetals, many porous products are now being made and have achieved a wideuse as filter elements, but many more valuable applications may be foundfor porous metals if the permeability to a gas or a liquid of a givenporous metal object can be accurately controlled and varied from onearea to another.

It is, therefore, an object of this invention to provide a porous metalobject having a wall of varying and controlled permeability from onearea to another.

Another object of this invention is to provide a porous metal objectwhich is differentially permeable and which may be produced with lessexpense.

A further object of this invention is to provide a porous metal wall forflow therethrough whose permeability may be more accurately controlled.

Additional objects, advantages and features of invention reside in theconstruction, arrangement, and combination of parts involved in theembodiments of the invention and its practice otherwise as will beunderstood from the following description and accompanying drawingwherein:

FIGURE 1 is a section taken through a fragment of a porous metal wall ofvarying or differential permeability according to this invention;

FIGURES 2, 3, 4, 5 and 6 are bottom views of a fragment of a wallsimilar to that shown in FIGURE 1, these figures showing several of manypossible patterns which may be formed by the impermeable layer of metalof this invention;

FIGURE 7 shows the configuration of a fragment of a wire screen with avarying mesh;

FIGURE 8 shows the wire screen of FIGURE 7 ernatent bedded in a wall ofporous material to vary and control the peremability of the wall fromone area to another;

FIGURE 9 is a cross section through a wall of porous rnetal and animpermeable layer of metal bonded thereto with apertures formed in theimpermeable layer and spaced apart to indicate a limitation of thisinvention;

FIGURE 10 is a side view of an air roller according to this inventionwith a fragment of one side of the roller broken away in section to showinterior construction and with a piece of plastic tape, shown insection, passing about the air roller;

FIGURE 11 is a longitudinal vertical section through a molten glassdelivery chute fabricated according to this invention;

FIGURE 12 is a section taken on line 1212 of FIG- URE 11;

FIGURE 13 is a longitudinal, vertical section through an upstandingliquid applying coating roller with an attached liquid feed tankaccording to this invention with a fragment of a vertical strip shownbeing coated and passing behind the roller; and

FIGURE 14 is a transverse vertical section through a glass mold formedaccording to this invention.

Referring to the drawing in detail, FIGURES 1 and 2 show a firstembodiment of this invention. As one example, a thin sheet of stainlesssteel 21 may have a large number of equal sized apertures 22 formed init. In the manner which has been described, coated grains of finestainless steel powder are compressed on top of the sheet 21 to form aneven layer thereon. Sheet 21 and the overlying layer of pressedstainless steel powder are then sintered to bond the individual grainsof powder together and to sheet 21 to form the porous and uniformlypermeable layer 20 as shown in FIGURE 1. When a gas or a liquid ispassed through the wall shown in FIG- URE 1 from bottom to top, theapertures 22 in the center of sheet 21 meter or pass more liquid or gasthan do the apertures 22 at the edges of sheet 21 because the apertures22 are disposed more closely together in the center of sheet 21. At theedges of sheet 21 where the apertures 22 are spaced further apart, theypermit less flow through them in a given area. Thus flow through theporous layer 20 of FIGURE 1 is controlled and varied from its center toits edges.

FIGURE 9 shows a layer of permeable material or porous metal 25 to whichthere is bonded a perforated layer of impermeable material 26. Layer 26is shown containing the apertures 27, 28 and 29. The dotted lines abovethese apertures in porous layer 25 indicate zones within layer 25 withinwhich gas or liquid how therethrough will vary less than 25 percent.Since the apertures 27 and 28 are spaced closer together than thethickness of the layer 25 above them, the flow or seepage of gas orliquid from the downstream side or top of layer 25 at points 30 and 31will not vary more than 25 percent. Since the apertures 28 and 29 arespaced further apart than the thickness of layer 25 above them, almostno gas or liquid will seep or flow from the upper surface of layer 25 atpoint 3-2. Thus when apertures in the impermeable layer 26 are furtherapart than the thickness of the porous layer above them, dead spots oflittle or no flow result on the downstream side of layer 25. These deadspots or the uneven seepage from the downstream side of the porous layerrender this invention unsuitable for the applications which will bedescribed hereafter. Thus despite the fact that conditions may varygreatly with different circumstances of temperature, pressure, porosity,the viscosity of the diffusing gas, etc., the maximum distance betweenopen areas of the impermeable layer of this invention must not begreater than the thickness of the porous metal layer on the downstreamside of the impermeable layer. When this limitation is observed, analmost constant seepage emerges from the entire downstream surface ofthe porous layer although the flow rate from a given area is controlledby the openings in the impermeable metal layer.

Further, the cost advantage of this invention becomes particularlyeffective when the pore size of the porous metal layer must be less than.005". With larger pore sizes, finely drilled plates may be substitutedfor the porous wall of this invention. However, it is very difiicult todrill or'form small holes and space them to control flow therethroughand such tine drilling is prohibitively expensive.

When a particular application requires a very small pore size from .005down to .0001" or even smaller, drilled plates cannot be fabricated atany cost to be substituted for the construction of this invention.

Referring further to FIGURES l and 2, the object of this invention couldbe made by first forming a layer or wall of porous metal and then silkscreening or otherwise depositing on the upstream side of layer 20 apattern of wax, grease, or other non-conducting material. If dots werescreened on the upstream side of layer 26 in a pattern shown by theapertures 22 of FIGURE 2, a metal layer 21 could then be plated on layer20 to create the impermeable metal layer 21. The non-conducting materialwould then be dissolved, melted or washed away leaving the apertures 22.Naturally, if the entire layer 20 of conducting porous metal wereimmersed in a plating solution, the downstream side of layer 20 wouldhave to be solidly coated with a non-conducting layer which would laterbe removed.

Still another way in which the layer 21 may be formed is to take a layer20 of porous metal and peen, machine or otherwise compact its upstreamsurface. This peenin'g 'or machining exerts a localized force tocompress the particles of the porous metal to render them into a solidlayer which is impermeable. This impermeable layer may then be coveredwith wax in a pattern leaving openings where it is desired to have theopenings 22. Acid may then be applied to the wax where it will etchthrough the impermeable peened layer 21 to form the apertures 22.

The wax coating may then be removed.

Many other porous metals besides stainless steel may be used in thepractice of this invention. For example,

pure nickel powder may be compacted and sintered at a temperature of2300 F. to form a porous layer 20. This nickel layer 20 may be sinteredon a nickel foil layer 21 containing suitable perforations or openings22. Inconel powder may be compacted and sintered at a temperature of2300 F., Monel metal powder may be compacted and sintered at atemperature of 2200 F., bronze powder may be compacted and sintered at atemperature of 1750 F. If the porous layer 20 is compacted on andsintered on a perforated metal sheet 21, this sheet should have a higheror the same melting point as the metal powder.

Many other patterns of openings in the impermeable metal layer may beprovided. FIGURE 2 shows an impervious layer 21 containing a largenumber of apertures of the same size which are spaced closer together orfurther apart in the impermeable layer to differentially meter flowthrough the porous layer extending downstream from them.

FIGURE 3 shows a modification of this invention in which an impermeablelayer 40 has a number of apertures 41 formed in it with the centers ofthe apertures 41 spaced the same distance apart from each other.Increased flow may take place through the apertures 41 on the left handside of FIGURE 3 because these apertures 41 are formed with a largerdiameter. Flow decreases to the right side of FIGURE 3 as the aperturesare made smaller to control and reduce flow through them.

FIGURE 4 shows a further modification of this invention in which aporous metal layer 44 has associated with it on its upstream side adiscontinuous impermeable metal layer 45 consisting of the round dots 46of metal which may be plated or other-wise fixed to layer 44. Flowthrough layer 44 is differentially metered or controlled according tothe size of the dots 46. Thus, as shown in FIGURE 4, the smaller dots 46on the left permit more flow past them than do the larger dots on theright side.

FIGURE 5 shows a layer of porous metal 48 which has an impermeable layer49 fixed to its upstream side in the form of the tapering strips 50. Asthe spaces 51 between the strips 50 become narrower towards the right ofFIG- URE 5, they progressively reduce and meter flow therethrough.

FIGURE 6 shows another of many possible patterns 55 which could beplated on a porous metal layer 56 to differentially control flowtherethrough.

In a like manner, as shown in FIGURES 7 and 8, a screen 58 may be wovenfrom longitudinal metal strips or wires 59 across which there are woventhe transverse strips or wires 60. The transverse strips 60 may bespaced closer together, as at the bottom of FIGURES 7 and 8, to moregreatly restrict and meter fluid flow past them. The screen 58 is bondedand sintered within a layer of porous metal 61 to render itdifferentially permeable and control flow therethrou-gh.

FIGURE 10 shows an air roller which illustrates one use to which thedifferentially permeable wall of this invention may be put. The airroller 62 is made in the following manner. A length of metal tubing 63has the closely spaced metering apertures 64 drilled or otherwise formedin it. The length of tubing 63 then has a cylindrical layer of porousmetal 65 compacted and then sintered about it. End members 67 and 68close the ends of the air roller 62 and may be welded or otherwise fixedin place. A pump 69 forces air through pipe 70 into the air roller 62.

If a length of plastic tape 71, which could be magnetic recording tapeduring the coating stage of its fabrication or which could be motionpicture film being coated with emulsion or developer, or the like, is topass about and be guided by air roller 62, it is desirable to have agreater amount of air escape at the center of air roller 62 to providean effect similar to the crown on a conventional flat belt pulley. Thusthe apertures 64 in the metal tube 63 are spaced more closely togetherin the center of air spool 62. This closer spacing passes more airthrough the porous metal layer 65 to provide a crown effect whichpositions strip 71 laterally as it passes over air roller 62.

For ordinary applications, an air roller may merely consist of a pieceof tubular material through which small apertures are drilled and spacedto provide more air where needed. However, as shown in FIGURE 10, theinner or bottom surface of tape 71 may have to have been freshly coatedwith a liquid such as an emulsion or developer during processing. Thepassing of tape 71 over pressurized air holes, even extremely fineholes, will cause a rippling of a still liquid coating on the rollerside of tape 71. However, the layer 65 of porous metal having a smallpore size and being thicker than the maximum distance between theapertures 64 ensures that air emerges or seeps from the surface ofroller 62 so smoothly that it will not ripple liquid on the underside oftape 71.

FIGURES l1 and 12 show a glass delivery chute which illustrates anotheruse to which the differentially permeable wall of this invention may beput. A glass delivery chute 72 has a trough formed from a layer ofporous metal 73 which is bonded within and lines an outer impermeablelayer 74. Layer 74 contains apertures 75. An outer casing 76 extendsabout the impermeable layer 74 so that the outer casing may bepressurized by means of an air pump or blower 77. When a deliveryapparatus 78 drops a globule of molten glass to charge a glass moldingmachine or the like in the chute 72, air escaping from the porous innersurface of layer 73 supports the globule 79 of molten glass.

As shown in FIGURE 11, globule 79 requires greater air support where itstrikes the upper portion of chute 72. It also requires greater supportwhere it is conducted in a curved path than it does in the lowerstraight portion of chute 72. Thus the upper portion of the impermeablelayer 74 contains more closely spaced or larger apertures 75 to meter alarger quantity of air therethrough. The lower portion of chute 72conducting the globule of molten glass 79 in a straight path requiresless air to support it, thus the lower portion of the impermeable layer74 contains more widely spaced or smaller apertures. The even flow andescape of air through the layer of porous metal 73 of this inventionprevents undesirable rippling or distortion of the glass globule 79.

Referring now to FIGURE 13, a further use for the differentiallypermeable porous metal wall of this invention is shown. It is oftendesirable to distribute glue or another liquid evenly on a strip orsheet 80 which is in a vertical position. Sheet 80 could be plasticbefore being laminated, it could be film being coated with developer,and the like. Strip 80, in a vertical position, passes the upstandingcoating roller 81. Roller 81 consists of a tubular impermeable layer 82containing the metering apertures 83. Sintered to the metal tube 82 is aporous cylindrical layer 84. A lower end cap 85 closes roller 81 and hasa shaft 86 projecting down from it which is rotatably fixed in a bearing87. A top plate 88 having a suitable seal 89 is entered by the tube 90which conducts a coating fluid 91 from a tank 92 into the coating roller81.

If the vertical coating roller 81 was made from a uniformly porousmetal, the greater hydraulic pressure of the coating fluid 91 at thebottom of the roller 81 would deposit a thicker layer of liquid on thesheet 80. However, the apertures 83 are spaced further apart or madesmaller at the bottom of coating roller 81 to counteract the increasedhydraulic pressure and thus insure that sheet 80, although in a verticalposition is uniformly coated with fluid 91.

One additional application for the differentially permeable wall of thisinvention will be described. Some glass articles are formed in what areknown as paste molds. These molds come in two or more parts and havetheir interior mold surfaces coated with graphite, burnt cork, burntwood chips, or the like. These coatings are very closely guarded secretsheld by glass molders. When the paste mold is opened, a few drops ofwater are introduced into the mold cavity to be sucked up by theinterior coating. A bubble of rotating molten glass is then blown intothe cavity from a rotating nozzle. Heat from the molten glass flashesmoisture in the graphite or other coating into steam which forms apillow or air bearing for the rotating glass which then cools. This is aparticularly critical operation as temperature is very important. If theglass is too hot or if insufficient steam is generated, the glass willstick within the mold. If there is too much steam, it will check orcraze the glass surface. The paste molding of glass is costly as themold cavity coating wears and must be constantly replaced.

FIGURE 14 shows a glass mold according to this invention. This glassmold 99 consists of two halves 100 and 101 each having a mold cavityformed in porous metal 102 and 103. Bonded to or associated with theouter sides of the two porous metal mold cavities 102 and 103 are theimpermeable layers 104 and 105 containing the metering apertures 106 and107. Both halves 100 and 101 of the mold cavity are surrounded by asuitable outer casing 106' which is formed in two parts 107' and 108'.In some mold situations vent pipes 109 should be provided every halfinch to one inch within the mold cavity to lead to the atmosphere beyondthe casing 106'. A conventional spinning glass blowing nozzle 110 isprovided to enter the top of the mold cavity. A duct 111 leads from apiston 112 and a cylinder 113 into the outer casing 106.

The glass mold 99 of this invention is used as follows. The mold halves100 and 101 are closed and the rotating glass blowing nozzle or pipe 110is introduced spinning into the mold cavity. As a charge of molten glassis blown spinning into the mold cavity, piston 112 is forced downwardwithin cylinder 113 to drive steam into the outer casing 106. This steamis thus forced through the apertures 106 and 107 and the porous metallayers 102 and 103 to cushion the spinning molten glass 120 with slightclearance from the sides of the mold cavity. Excess steam may flow frombetween the spinning molten glass and the mold cavity through the ventpipes 109 as it does in the conventional paste mold. When the blownglass 120 solidifies, mold 99 is opened and the finished article removedas in the conventional paste mold. Any suitable means (not shown) maybeprovided to generate steam to be introduced into casing 106.

In some applications, superior results may be obtained by introducingsuperheated air by means of piston 112 into the outer casing 106. Thissuperheated air may prevent the overly rapid solidification of thinnerwalled sections of the blown glass article as well as supporting itwithin the mold cavity. Since different quantities of steam or hot airmust be introduced through different parts of the porous metal moldcavity, the flow through the mold cavity is controlled by forming largerand smaller apertures 106 and 107 in the impermeable layers 104 and 105or by spacing apertures 106 and 107 closer or further apart. Thus thisinvention allows mold conditions within a glass molding cavity to beeven more closely controlled than it is possible in a conventional pastemold.

Drilled apertures could not be used leading into a mold cavity of thisinvention as the flow of a gas, whether steam or superheated air,through apertures would mark the surface of the spinning and coolingglass article. Further, dead spots or uneven seepage of air or steamfrom the inner surface of the porous mold cavity will also mark thesurface of the glass object being molded and may tend to cause it tostick to the surface of the mold cavity. Thus the porous wall of thisuse of my invention requires that the thickness of the porous layer 102or 103 over a given pair of apertures 106 or 107 must be greater thanthe distance apart of the apertures 106 or 107.

While this invention has been disclosed in the best forms known to me,it is nevertheless to be understood that these are purely exemplary andthat modifications may be made without departing from the spirit of theinvention except as it may be more limited in the appended claimsWherein I claim:

1. A porous wall for differential flow therethrough, said 'Wallcomprising a porous metal layer having an upstream and a downstreamside, and an impermeable layer associated with the upstream side of saidporous metal layer, said impermeable layer containing openings meteringdifferent amounts of flow therethrough in different portions of saidimpermeable layer, said porous metal layer being thicker on thedownstream side of openings in said impermeable layer than the distancebetween openings. 1

2. The combination according to claim 1 wherein the pore size of saidporous metal layer is less than .005".

3. A porous wall for differential flow therethrough, said wallcomprising a porous metal layer having an upstream and a downstreamside, and a thin metal plate or sheet associated with the upstream sideof said porous metal layer, said metal sheet containing aperturesmetering different amounts of flow therethrough in different portions ofsaid metal sheet, said porous metal layer being thicker on thedownstream side of any given pair of apertures in said sheet than thedistance between the apertures.

4. A porous Wall for differential flow therethrough,

said wall comprising a porous metal layer having an upstream and adownstream side, and a metal sheet associated with the upstream side ofsaid porous metal layer, said metal sheet containing apertures of thesame size spaced different distances apart to meter different amounts offlow therethrough in different portions of said metal sheet, said porousmetal layer being thicker on the downstream side of any given pair ofapertures in said metal sheet than the distance between the apertures.

5. A porous wall for differential flow therethrough, said wallcomprising a porous metal layer having an upstream and a downstream sideand a metal sheet associated with the upstream side of said porouslayer, said metal sheet containing apertures of different sizes meteringdifferent amounts of flow therethrough in different portions of saidimpermeable layer, said porous metal layer being thicker on thedownstream side of any given pair of apertures than the distance betweenthe apertures.

6. A porous wall for differential flow therethrough, said Wallcomprising a porous metal layer having an upstream and a downstreamside, and an impermeable metal layer plated on the upstream side of saidporous metal layer, said impermeable layer containing openings meteringdifferent amounts of flow therethrough in different portions of saidimpermeable layer, said porous metal layer being thicker on thedownstream side of openings in said impermeable layer than the distancebetween openings.

7. A porous wall for differential flow therethrough, said wallcomprising a porous metal layer having an upstream and a downstreamside, and an impermeable peened surface on the upstream side of saidporous metal layer, said impermeable peened surface containing openingsmetering different amounts of flow therethrough in different portions ofsaid impermeable peened surface, said porous metal layer being thickeron the downstream side of openings in said impermeable peened surfacethan the distance between openings.

8. An air roller comprising, in combination, metal tubing containingclosely spaced metering apertures metering a greater amount of flow inthe center portion of the metal tubing, a cylindrical layer of porousmetal compacted and sintered about the metal tubing with a thicknessgreater than the maximum distance between the metering apertures in saidmetal tubing, the cylindrical layer of porous metal having a pore sizeless than .005, closures for the ends of the metal tubing and thecylindrical layer of porous metal, and means introducing pressurized airwithin the metal tubing.

9. A glass delivery chute comprising, in combination, a trough formedfrom a layer of porous metal, an impermeable layer extending about saidtrough of porous metal, said impermeable layer containing openingsmetering different amounts of flow therethrough to different portions ofsaid trough of porous metal, said trough of porous metal being thickerabove openings in said impermeable layer than the distance betweenopenings, an outer casing extending about said impermeable layer, and

means introducing pressurized air into said outer casing.

said impermeable layer containing openings metering different amounts offlow therethrough in different portions of said impermeable layer, saidcylindrical layer of porous metal being thicker outside openings in saidimpermeable layer than the distance between openings, means closing theends of said cylindrical layer of porous metal, means rotatably mountingsaid cylindrical layer of porous metal, and means introducing a coatingfluid within said cylindrical layer of porous metal to be meteredthrough the openings of said impermeable layer and emerge from the outersurface of the cylindrical layer of porous metal.

11. The combination according to claim 10 in which said coating rolleris upstanding and in which openings in the lower end of said impermeablelayer more greatly restrict flow therethrough to compensate forincreased hydraulic pressure of the coating fluid within the coatingroller so that the coating fluid emerges evenly from the outer surfaceof the coating roller.

12. A glass mold comprising, in combination, a multipart porous metalmold having a central cavity, outer impermeable metal layers extendingabout the multipart porous metal mold, said outer layers containingopenings metering different amounts of flow therethrough in differentportions of said outer layers, said multipart porous metal mold beingthicker to the inside of the opening than the distance between openings,an outer casing extending about the porous metal mold, a glass blowingpipe entering said central cavity of said porous metal mold, and meansintroducing a gas into said outer casing to flow through the openings insaid impermeable layers and the porous metal mold to enter the centralcavity and provide temperature control and a gas cushion within thecentral cavity during the molding cycle.

13. A porous wall for differential flow therethrough, said wallcomprising a woven screen of varying mesh size from one portion of saidscreen to another, and a layer of porous material bonded to said screen.

14. A porous wall for differential flow therethrough, said wall havingan upstream and a downstream side and comprising a woven metal screenhaving parallel evenly spaced longitudinal members and transversemembers woven across said longitudinal members, some of said transversemembers being woven across said longitudinal members closer to eachother to restrict flow therebetween, and a layer of porous metal bondedto the downstream side of said screen.

References Cited by the Examiner UNITED STATES PATENTS 2,455,804-12/1948 Ransley 29191.2 2,737,456 3/1956 Haller 75-200 2,846,759 8/1958Foley 29--l91.2 2,872,311 2/1959 Marshall et al 75-200 2,888,742 6/1959Stumbock 29-182.3

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, R. O. DEAN, Assistant Examiners.

1. A POROUS WALL FOR DIFFERENTIAL FLOW THERETHROUGH, SAID WALL COMPRISING A POROUS METAL LAYER HAVING AN UPSTREAM AND A DOWNSTREAM SIDE, AND AN IMPERMEABLE LAYER ASSOCIATED WITH THE UPSTREAM SIDE OF SAID POROUS METAL LAYER, SAID IMPERMEABLE LAYER CONTAINING OPENINGS METERING DIFFERENT AMOUNTS OF FLOW THERETHROUGH IN DIFFERENT PORTIONS OF SAID IMPERMEABLE LAYER, SAID POROUS METAL LAYER BEING THICKER ON THE DOWNSTREAM SIDE OF OPENINGS IN SAID IMPERMEABLE LAYER THAN THE DISTANCE BETWEEN OPENINGS. 